1. Field of the Invention
The present invention relates to an exposure method for producing a liquid crystal display device or a semiconductor device, and more particularly an exposure method for forming patterns of plural layers in superposed manner on a substrate, or exposing a large-sized substrate to small pattern area in mutually connected manner for obtaining a large-sized device.
2. Related Background Art
For forming a large-sized liquid crystal display device or the like on a substrate, there has been employed a method of providing small pattern area in continuation on the substrate, by means of a step-and-repeat projection exposure apparatus. However, because of the imaging characteristics of the projection optical system, such as distortion aberration, the continuous (junction) portion of the adjacent small pattern areas may be aberrated from the proper junction state in which the pattern is formed in continuous state. In case of such "aberration" or low precision of junction, the performance of device in such area becomes deteriorated in comparison with that of other areas, and there may eventually result a difference in image contrast or in color, detectable by the human eyes.
Also in the formation of a device there is often conducted the exposure of a pattern in superposition on an already exposed pattern. The above-mentioned deterioration of the performance of the device will also occur in such case if the precision of such pattern superposition is not adequate.
In order to improve the precision of junction or superposition of the pattern areas, there has been employed a method of detecting the aberration of a representative position (representative point) in the actually exposed pattern and determining the correcting parameters so as to minimize said aberration. More specifically, in the junction or superposition of the pattern areas, there is employed a reticle provided with a vernier pattern in the vicinity of the pattern area, whereby said vernier pattern is exposed also in superposition, and the correcting parameters (amount of two-dimensional shifts and rotation of the photosensitive substrate) are determined so as to minimize the reading of said vernier pattern, for example by the minimum square method.
However, such conventional technology, being based on the imaging characteristics of limited representative points in the projection area of the projection optical system, is incapable of sufficient correction on the image which is different in position from such representative points. Also in case of superposing patterns to be exposed utilizing mutually different partial areas within the projection area, there is required a precise correction for such partial areas, but, in the conventional technology, the correction for such partial areas is unsatisfactory because the correction is made only on said representative points in the projection area. A same situation occurs also when the patterns are superposed with different plural projection optical systems.
Furthermore, in case of exposing plural patterns in mutual junction, said patterns cannot be connected with a sufficient precision, since the partial areas, corresponding to the junction portion, within the projection area are different in the state of correction.
Furthermore, the patterns constituting the device have an extending direction (X, Y directions), and, in certain device structures, the performance of the device depends on this direction. For this reason it is sometimes required, not only to improve the precision of junction or superposition, or the precision of superposition of the junction portion, in the X- and Y-directions, but also to achieve a particularly high precision in a specified direction. Also in such case, the conventional technology, designed to determine the correcting parameters only by the representative points predetermined in consideration of the directions requiring precision and those not requiring precision, is incapable of sufficient correction for such direction requiring a particularly high precision.